Illegal billing usage

My phone number is : 9883225162
I bought a Nokia Lumia Handset in January 14, 2012, and once I entered my vodafone postpaid sim, 2GB of 3G data free for 4months was activated. Accordingly it should end on 14th May. But when I checked from the Vodafone Store on 29th April, 2012, I was told that my free period ended on 21st April.
But unfortunately I was not notified of the end of this service and neither was this service deactivated.
Vodafone charged me at the rate of 5p/10 kb and for using only 343 MB of data, I am charged Rupees 2200 ruppes for using only 340 mb of data(which is much above the normal standard rate).

I submitted a complaint in vodafone store on 22nd may in vodafone dlf store and they said within 3 days the amount will be waived fully or atleast most of it and will be notified within 3 days(My colleague was with me present at the time of this discussion).
I wasn’t notified within 3 days and then I called after that, they said within 24 hours somebody will call from the billing team and take necessary actions and this happened till 4th June when I gave a final ultimatum, within that day somebody called me up and they said they will waive the amount and told me to a person named mohit dhawan to regenerate a new bill. Unfortunately, again nobody responded and another person called me up and asked me the same problem again(on 6th June,2012). He said within 24 hours, the issue will be solved and someone will call me up and give me an updated bill. Now after 9th June, the billing period is over and Mr Mohit Dhawan from vodafone has responded that the charges are genuine and the bill won’t be waived.

I have my colleague who was with me when we went to the vodafone store and the person promised that it will be waived.
I have the call list of how much i suffered everyday for calling them up and asking for an update.
This is absolute cheating on the part of vodafone to first stopping the free period, and then charging such a huge amount without notification and then promising to waive and then continuously harrasing for the last 1 month without taking any action.
Please help

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